The monograph is organized around the following questions: 1) What are the "root causes" of terrorism? 2) Why and how do some individuals become terrorists? 3) How do terrorists generate and maintain support? 4) What determines terrorists’ decisions and behaviors (for example, what roles are played by ideology, religion, and rational choice)? 5) Why do individuals disengage or deradicalize? and 6) How can strategic communications be more effective? A chapter on the economics of terrorism reviews quantitative empirical reserch bearing on all of these questions. A chapter suggests ways to represent social-science knowledge analytically, but so as to be readily communicated. And, finally, a chapter looks across the other chapters to highlight particular cross-cutting topics of interest.